Among the processes known for preparing ibuprofen is that of European Patent Application 284,310 (Hoechst Celanese, published September 1988), which teaches that ibuprofen can be prepared by carboxylating 1-(4-isobutylphenyl)ethanol with carbon monoxide in an acidic aqueous medium and in the presence of a palladium compound/phosphine complex and dissociated hydrogen and halide ions, which are preferably derived from a hydrogen halide This process has the disadvantage of starting with 1-(4-isobutyl-phenyl) ethanol, a compound which is not economical to make by known processes.
Gardano et al. (U.S. Pat. No. 4,536,595, issued August, 1985) teach the preparation of alkaline salts of certain alpha-arylpropionic acids by reaction with carbon monoxide, at substantially ambient temperature and pressure conditions, of the corresponding arylethyl secondary halide in an anhydrous alcoholic solvent in the presence of alkaline hydroxides and, as catalyst, a salt of cobalt hydrocarbonyl.
Alper et al. in J. Chem. Soc. Chem. Comm., 1983, 1270-1271, discloses the alkenes can react with carbon monoxide, water, hydrochloric acid and a mixture of palladium and copper to produce the hydrocarboxylated product, branched chain carboxylic acid. Oxygen is necessary to succeed in the reaction. Subsequently, Alper et. al. have disclosed similar catalyst systems, but employing a chiral ligand, as being successful in asymmetric hydrocarboxylation reactions. See Alper et al., PCT Application, WO 9103,452, and J. Am. Chem. Soc., 112, 2803-2804 (1990).
The Invention
In the following specification, the meaning of the substituent groups is as follows: "alkyl" means straight or branched chain alkyl having 1 to 20 carbon atoms and includes, for example, methyl, ethyl, propyl, isopropyl, butyl, isobutyl, secondary butyl, tertiary butyl, pentyl, isopentyl, neopentyl, hexyl, heptyl, octyl, 2-ethylhexyl, 1,1,3,3-tetramethylbutyl, nonyl, decyl, dodecyl, tetradecyl, hexadecyl, octadecyl and eicosyl and the like (for the purposes of this definition, "alkyl" is also "aliphatic");
"cycloalkyl" means cyclic alkyl having 3 to 7 carbon atoms and includes cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl and the like;
"substituted aryl" means phenyl or naphthyl substituted by at least one substituent selected from the group consisting of halogen (chlorine, bromine, fluorine or iodine), amino, nitro, hydroxy, alkyl, alkoxy which means straight or branched chain alkoxy having 1 to 10 carbon atoms, and includes, for example, methoxy, ethoxy, propoxy, isopropoxy, butoxy, isobutoxy, secondary butoxy, tertiary butoxy, pentyloxy, isopentyloxy, hexyloxy, heptyloxy, octyloxy, nonyloxy and decyloxy, aryloxy including phenoxy and phenoxy substituted with halo, alkyl, alkoxy and the like, haloalkyl which means straight or branched chain alkyl having 1 to 8 carbon atoms which is substituted by at least one halogen, and includes, for example, chloromethyl, bromomethyl, fluoromethyl, iodomethyl, 2-chloroethyl, 2-bromoethyl, 2-fluoroethyl, 3-chloropropyl, 3-bromopropyl, fluoropropyl, 4-chlorobutyl, 4-fluorobutyl, dichloromethyl, dibromomethyl, difluoromethyl, diiodomethyl, 2,2-dichloroethyl, 2,2-diibromoethyl, 2,2-difluoroethyl, 3,3-dichloropropyl, 3,3-difluoropropyl, 4,4-dichlorobutyl, 4,4-difluorobutyl, trichloromethyl, trifluoromethyl, 2,2,2-trifluoroethyl, 2,3,3-trifluoropropyl, 1,1,2,2-tetrafluoroethyl, 2,2,3,3-tetrafluoropropyl and the like;
"alkyl-substituted cycloalkyl" means that the cycloalkyl moiety is cyclic alkyl having 3 to 7 carbon atoms and the alkyl moiety is straight or branched chain alkyl having 1 to 8 carbon atoms, and includes, for example, cyclopropylmethyl, cyclobutylmethyl, cyclopentylmethyl, cyclohexylmethyl, cycloheptylmethyl, 2-cyclopropylethyl, 2-cyclopentylethyl, 2-cyclohexylethyl, 3-cyclopropylpropyl, 3-cyclopentylpropyl, 3-cyclohexylpropyl, 4-cyclopropylbutyl, 4-cyclopentylbutyl, 4-cyclohexylbutyl, 6-cyclopropylhexyl, 6-cyclohexylhexyl and the like;
"alkylthio" means a divalent sulfur with alkyl occupying one of the valencies and includes the groups methylthio, ethylthio, propylthio, butylthio, pentylthio, hexylthio, octylthio and the like;
"heteroaryl" means 5 to 10 membered nono- or fused-heteroaromatic ring which has at least one heteroatom selected from the group consisting of nitrogen, oxygen and sulfur, and includes, for example, 2-furyl, 3-furyl, 2-thienyl, 3-thienyl, 2pyridyl, 3-pyridyl, 4-pyridyl, pyrazolyl, imidazolyl, pyrimidinyl, pyridazinyl, pyrazinyl, benzimidazolyl, quinolyl, oxazolyl, thiazolyl, indolyl and the like;
"substituted heteroaryl" means 5 to 10 membered mono or fused-heteroaromatic ring which has at least one heteroaromatic ring which has at least one heteroatom selected from the group consisting of nitrogen, oxygen and sulfur and which is substituted by at least one substituent selected from the group consisting of halogen, amino, nitro, hydroxy, alkyl, alkoxy and haloalkyl on the above-mentioned heteroaromatic nucleus;
"alkanoyl" means alkanoyl having 2 to 18 carbon atoms and includes, for example, acetyl, propionyl, butyryl, isobutyryl, pivaloyl, valeryl, hexanoyl, octanoyl, lauroyl, stearoyl and the like;
"aroyl" means benzoyl or naphthoyl;
"substituted aroyl" means benzoyl or naphthoyl substituted by at least one substituent selected from the group consisting of halogen, amino, nitro, hydroxy, alkyl, alkoxy and haloalkyl on the benzene or naphthalene ring;
"heteroarylcarbonyl" means that the heteroaryl moiety is 5 to 10 membered mono- or fused-heteroaromatic ring having at least one heteroatom selected from the group consisting of nitrogen, oxygen and sulfur as mentioned above, and includes, for example, furoyl, thinoyl, nicotinoyl, isonicotinoyl, pyrazolylcarbonyl, imidazolylcarbonyl, pyrimidinylcarbonyl, benzimidazolylcarbonyl and the like;
"substituted heteroarylcarbonyl" means the above-mentioned heteroarylcarbonyl which is substituted by at least one substituent selected from the group consisting of halogen, amino, nitro, hydroxy, alkoxy and haloalkyl on the heteroaryl nucleus; and includes, for example, 2-oxo-i,3-dioxolan-4-ylmethyl, 2-oxo-1,3-dioxan-5-yl and the like.
The present invention embraces any racemates and individual optical isomers thereof of the compounds of the following formula (I) having a chiral carbon atom. ##STR1## where Ar, R.sub.1, R.sub.2, R.sub.3, R.sub.4 and R.sub.5 are subsequenty defined.
In accordance with the present invention, aryl-substituted aliphatic carboxylic acid esters are prepared by carboxylating an aryl-substituted, aliphatic halogen-containing compound with carbon monoxide in a neutral or acidic anhydrous medium containing at least 1 mol of a C.sub.1 to about C.sub.8 linear or branched aliphatic alcohol per mol of halogen-containing compound at a temperature of between about 25.degree. C. and about 200.degree. C. and a carbon monoxide pressure of at least about one atmosphere in the presence of a mixture of (i) palladium (O) or a palladium compound in which the palladium has a valence of 1 or 2 and (ii) a copper compound having a valence of 1 or 2 and at least one acid-stable ligand. An alcohol equivalent, such as the trialkyl orthoalkanoates, dialkyl-ketals, alkyl formates, trialkyl-borates, titanium (IV) alkoxides, etc. are also useful. The esters may be readily converted to the corresponding free carboxylic acids or salts by well known conventional methods.
The halogen-containing compound which is catalytically carboxylated in the practice of this invention has the formula: ##STR2## where X is halogen (fluoro chloro bromo iodo) or other leaving groups such as tosylate, acetate, mesylate etc., Ar is unsubstituted or substituted aryl and R.sub.2, R.sub.3, R.sub.4 and R.sub.5 are the same or different and are hydrogen, alkyl, cycloalkyl, substituted or unsubstituted aryl, alkoxy, alkylthio, substituted or unsubstituted heteroaryl, alkanoyl, substituted or unsubstituted aroyl, substituted or unsubstituted heteroarylcarbonyl, trifluoromethyl or halo. A wide variety of leaving groups are disclosed, for example, in March, Advanced Organic Chemistry, incorporated herein by reference.
Preferably, in the compounds of formula II, X is chloro or bromo, Ar is unsubstituted or substituted aryl, R.sub.2, R.sub.3, R.sub.4 and R.sub.5 are hydrogen, C.sub.1 to C.sub.2 alkyl, substituted or unsubstituted phenyl or trifluoromethyl.
Most preferably X is chloro, Ar is phenyl substituted with alkyl or naphthyl substituted with alkoxy, R.sub.2, R.sub.3, R.sub.4 and R.sub.5 are hydrogen, methyl or trifluoromethyl.
The catalytic carboxylation of the compound of formula II is conducted in an anhydrous medium (in the absence of water), at a temperature between about 25.degree. C. and about 200.degree. C., preferably about 50.degree.-150.degree. C., and most preferably about 80.degree.-130.degree. C. Higher temperatures can also be used. It has been found that a small advantage in yield is obtained by gradually increasing the temperature within the preferred ranges during the course of the reaction.
The partial pressure of carbon monoxide in the reaction vessel is at least about 1 atmosphere (14.7 psig) at ambient temperature (or the temperature at which the vessel is charged). Any higher pressures of carbon monoxide can be used up to the pressure limits of the reaction apparatus. A pressure up to about 3000 psig is convenient in the process. More preferred is a pressure from about 300 to about 3000 psig at the reaction temperature, and most preferred is a pressure from about 500 to about 1,500 psig. It should be noted that the presence of oxygen is undesirable in the carbonylation reaction of this invention. Hence, an atmosphere of 100% carbon monoxide is most preferred to carry out this process. Various inert gases can, however, be incorporated in the reaction mass (nitrogen, argon, etc.) the only criteria being that the process should not be slowed to the point of requiring exceptionally long periods to complete the reaction.
The carboxylation is conducted in the presence of at least about one mol of an anhydrous aliphatic alcohol per mol of the compound of formula II; however, an excess is preferred in order to assist in driving the reaction to completion. Although there is no real upper limit to the amount of alcohol except that imposed by practicality (e.g. the size of the reaction vessel), an amount up to about 100 mols per mol of the compounds of formula II is useful in the process. Further, controlling the amount of alcohol used in the process of this invention is advantageous in terms of producing the highest yields. Therefore, an amount from about 2 to about 50 mols of alcohol per mol of the compounds of formula II is preferred, and an amount from about 2 to about 10 mols of alcohol per mol of the such olefinic compound is most preferred. The product of the reaction is an carboxylic acid ester (where R.sub.1 is alkyl). These compound have the following formula: ##STR3## where R.sub.1 is hydrogen or alkyl and Ar, R.sub.2, R.sub.3, R.sub.4 and R.sub.5 are as previously defined.
Any alcohol which produces an ester of the carboxylic acid may be used in the practice of this invention. In a preferred embodiment, the lower aliphatic alcohols, are used. Examples of the alcohols to be used in this embodiment include methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-, iso- sec-, and tert-butyl alcohols, the pentyl alcohols, the hexyl alcohols, etc. Methyl alcohol is highly preferred, and ethyl alcohol is most highly preferred. Other alcohols, glycols, or aromatic hydroxy compounds and, further, any "source of alkoxide ions" may also be used. The source of such alkoxide ions is from a compound selected from the group consisting of HC(OR.sub.1).sub.3, (R).sub.2 C(OR.sub.1).sub.2, HC(O)OR.sub.1, B(OR.sub.1).sub.3, P(OR.sub.1).sub.3, Ti(OR.sub.1).sub.4, and Al(OR.sub.1).sub.3 where R is hydrogen or the same or different than R.sub.1 where R.sub.1 is as preViously defined. Examples of compounds that will produce alkoxide ions in the reaction solution used in the process of this invention are: trimethyl orthoformate, triethyl orthoformate, methyl formate, ethyl formate, trimethylborate, trimethylphosphite, titanium (IV) propoxide, titanium (IV) isopropoxide, titanium (IV) methoxide.
In a preferred embodiment of this invention, the carboxylation reaction is initiated under neutral conditions, i.e., with no added acid. It can also be performed in the presence of an added acid. When acids are added, such acids include sulfuric acid, phosphoric acid, sulfonic acids, or acetic or halo- substituted acetic acids. A hydrogen halide acid such as hydrochloric or hydrobromic acid is preferred. The hydrogen halide may be added as a gas phase or as a liquid phase (e.g., in the form of an alcoholic solution). Any concentration may be used. Hydrochloric acid is particularly preferred, at a concentration up to about 10%; more highly preferred is a concentration from about 10% to about 30%. The acidity of the carboxylation reaction mixture can be controlled by adding a buffering reagent (the side-products are reduced by controlling the acidity of the reaction mixture). Examples of buffering reagents used in the process of this invention are NaOAc, Na.sub.2 HPO.sub.4, NH.sub.4 Cl, HaHCO.sub.3. A variety of buffering reagents are disclosed in CRC, Handbook of Chemistry and Physics, incorporated herein by reference.
The catalytic carboxylation process of this invention is conducted in the presence of a reaction-promoting quantity of i) palladium(O) or a mixture of a palladium compound in which the palladium has a valence of 1 or 2 and ii) a copper compound, with at least one acid-stable ligand. Ligands which may be used include monodentate or multidentate electron-donating substances such as those containing elements P, N, O and the like, and those containing multiple bonds such as olefinic compounds. Examples of such acid-stable ligands are trihydrocarbylphosphines, including trialkyl- and triarylphosphines, such as tri-n-butyl-, tricyclohexyl-, and triphenylphosphine; lower alkyl and aryl nitriles, such as benzonitrile and n-propionitrile; ligands containing pi-electrons, such as an allyl compound or 1,5-cyclooctadiene; piperidine, piperazine, trichlorostannate(II), and acetylacetonate; and the like. In one embodiment, the palladium and copper are added as a pre-formed complex of palladium(II) chloride or bromide, copper(II) chloride or bromide and carbon monoxide or any other similar complex. In a preferred embodiment, active catalytic species are formed in situ (a homogeneous catalyst system) by the addition to the reaction mixture of the individual components, i.e., a ligand, a copper compound, and a palladium compound such as the inorganic salts of palladium(II) and copper(II) such as the chlorides, bromides, nitrates, sulfates, or acetates. In the most preferred embodiment, triphenylphosphine, copper(II) chloride, and palladium(II) chloride are used and are added individually or together, either simultaneously or sequentially.
Palladium and/or copper compounds can be supported on carbon, silica, alumnia, zeolite, clay, and other polymeric materials and used as the heterogeneous catalysts (the support is a solvent, insoluble material). Examples of palladium and/or copper support materials and catalysts used in the process of this invention are palladium on carbon, Pd(OH).sub.2 on carbon, Pd(II) exchanged Zeolite LZ-Y62, Pd(II) and Cu(II) exchanged clay montmorillonite KSF.
The amount of copper and palladium compounds or palladium metal and copper compounds preferably employed is such as to provide from about 4 to about 8000 mols of the compound of formula II per mol of the mixture of metal salts; more preferred is an amount to provide from about 10 to about 4000 mols of compound of formula II per mol of the mixture; the most preferred amounts provide from about 20 to 2000 mols of the compounds of formula II per mol of the mixture. The process of this invention is conducted in the presence of at least one mol of ligand per mol of the mixture of metal and metal salt of metal salts. More preferably about 2 to about 40 mols of ligand per mol of the mixture are present, and most preferably about 2 to about 20 mols of ligand per mol of mixture are used.
The presence of a solvent is not required in the process of this invention, although it may be desirable in some circumstances. Those solvents which can be used include one or more of the following: ketones, for example, acetone, methyl ethyl ketone, diethyl ketone, methyl-n-propyl ketone, acetophenone, and the like; linear, poly and cyclic ethers, for example, diethyl ether, di-n-propyl ether, di-n-butyl ether, ethyl-n-propyl ether, glyme (the dimethyl ether of ethylene glycol), diglyme (the dimethyl ether of diethylene glycol), tetrahydrofuran, dioxane, 1,3-dioxolane, and similar compounds; aliphatic or aromatic carboxylic esters, for example, methyl formate, methyl acetate, methyl 2-(4-isobutylphenyl)propionate (PME), methyl benzoate, and similar compounds; and aromatic hydrocarbons, for example, isobutylbenzene (IBB), toluene, ethyl benzene, xylenes, and similar compounds. Alcohols are also suitable as solvents, for example, methanol, ethanol, 1-propanol, 2-propanol, isomers of butanol, isomers of pentanol, etc. Acids and esters may also be used, such as formic or acetic acid or ethyl acetate, etc. When an ester or an alcohol is used as solvent, the product is the corresponding ester of the carboxylic acid. Most highly preferred are ethers, especially dioxane and glyme. When solvents are used, the amount can be up to about 100 mL per gram of the compounds of formula II, but the process is most advantageously conducted in the presence of about 1 to 30 mL per gram of the compound of formula II.
In those specific embodiments of this invention in which an ester of ibuprofen is produced, the ester may be conveniently converted to the acid (ibuprofen itself) by conventional methods of hydrolysis.
The following examples are given to illustrate the process of this invention and are not intended as a limitation thereof.